Prevention by Estrogen of the Decidual Alkaline Phosphatase Response in Intact and Ovariectomized Pseudopregnant Rats

Summary The decidual alkaline phosphatase of traumatized intact pseudopregnant rats was 10–15 times greater on day 8 than nondecidualized uteri. This effect was not altered by treatment of (a) intact rats with 5 mg of progesterone and/or 17β-estradiol, 0.1 μg on days 1–3, 1.0 μg on days 4–7, daily, and (b) castrated animals with the progestin (days 1–7) alone or combined with either the above estrogen regimen, or a single 1.01 μg dose of 17β-estradiol on days 3, 4, or 5. If 1.0 μg of 17β-estradiol was administered with or without progesterone for days 1–7, no decidualization or rise in alkaline phosphatase was noted. Similarly, the enzyme failed to increase in nondecidualized castrated rats receiving the 0.1 μg on days 1–3, 1.0 μg on days 4–7, estrogen regimen. The data demonstrate that the decidual alkaline phosphatase response is independent of circulating ovarian estrogen. Estrogen (0.1 μg on days 1–3 or 4, 1.0 μg on days 4 or 5–7) appeared to reduce the number of intact rats exhibiting decidualization and enhanced enzyme activity.